Certain blood specimens are photosensitive and should be protected from light. Bilirubin, beta-carotene, and porphyrins among others are such blood constituents that break down in the presence of light. The blood specimens for photosensitive analytes should be collected in commercially available brown or amber colored tubes which do not allow light to enter (see an example in the picture to the right). If such tubes are not available, the tube should be wrapped in aluminum foil.